Uso do índice de suficiência de nitrogênio na estimativa da necessidade de adubação nitrogenada em feijoeiro

Chlorophyll determination with a portable chlorophyll meter can indicate the period of highest N demand of plants and whether sidedressing is required or not. In this sense, defining the optimal timing of N application to common bean is fundamental to increase N use efficiency, increase yields and reduce the cost of fertilization. The objectives of this study were to evaluate the efficiency of N sufficiency index (NSI) calculated based on the relative chlorophyll index (RCI) in leaves, measured with a portable chlorophyll meter, as an indicator of time of N sidedressing fertilization and to verify which NSI (90 and 95 %) value is the most appropriate to indicate the moment of N fertilization of common bean cultivar Perola. The experiment was carried out in the rainy and dry growing seasons of the agricultural year 2009/10 on a dystroferric Red Nitosol, in Botucatu, São Paulo State, Brazil. The experiment was arranged in a randomized complete block design with five treatments, consisting of N managements (M1: 200 kg ha-1 N (40 kg at sowing + 80 kg 15 days after emergence (DAE) + 80 kg 30 DAE); M2: 100 kg ha-1 N (20 kg at sowing + 40 kg 15 DAE + 40 kg 30 DAE); M3: 20 kg ha-1 N at sowing + 30 kg ha-1 when chlorophyll meter readings indicated NSI < 95 %; M4: 20 kg ha-1 N at sowing + 30 kg ha-1 N when chlorophyll meter readings indicated NSI < 90 % and, M5: control (without N application)) and four replications. The variables RCI, aboveground dry matter, total leaf N concentration, production components, grain yield, relative yield, and N use efficiency were evaluated. The RCI correlated with leaf N concentrations. By monitoring the RCI with the chlorophyll meter, the period of N sidedressing of common bean could be defined, improving N use efficiency and avoiding unnecessary N supply to common bean. The NSI 90 % of the reference area was more efficient to define the moment of N sidedressing of common bean, to increase N use efficiency.The authors are indebted to the State of São Paulo Research Foundation (FAPESP) for financial support and a scholarship of the first author, and to the National Council for Scientific and Technological Development (CNPq) for scholarships of the second author.

Piatã palisadegrass morphogenic, nutritional and productive parameters related to nitrogen and sulphur

O cultivar Piatã de Brachiaria brizantha é uma gramínea forrageira de lançamento recente para uso nas pastagens brasileiras e a pesquisa relativa à nutrição mineral deste capim é escassa. O nitrogênio é o principal responsável pelo aumento da produtividade em plantas forrageiras, porém a associação com o enxofre pode influir nas respostas das plantas forrageiras à adubação. Mediante a combinação de doses de nitrogênio com doses de enxofre, objetivou-se estudar as características morfogênicas, nutricionais e produtivas do capim-piatã cultivado em solução nutritiva, empregando-se a sílica como substrato. O experimento foi realizado em casa de vegetação e estudou cinco doses de nitrogênio (2; 9; 16; 23 e 30 mmol L-1) e cinco doses de enxofre (0,1; 0,7; 1,3; 1,9 e 2,5 mmol L-1), em esquema fatorial 52 fracionado, em delineamento de blocos casualizados, com quatro repetições. As plantas foram submetidas a dois cortes, sendo o primeiro aos 44 dias após o transplantio e o segundo 25 dias após o primeiro corte. A interação doses de nitrogênio x doses de enxofre foi significativa para o número total de folhas e perfilhos, taxa de aparecimento de folhas e filocrono, área foliar, massa seca da parte aérea e das raízes, valor SPAD, comprimento e superfície radiculares totais, concentração de nitrogênio e de enxofre nos tecidos foliares e radiculares, concentração de nitrato e relação nitrogênio total:enxofre total (Nt:St) em pelo menos um dos dois ciclos de crescimento do capim-piatã. As mais elevadas doses de nitrogênio e de enxofre maximizaram o crescimento e desenvolvimento da parte aérea e do sistema radicular das plantas. Doses elevadas de nitrogênio diminuíram o comprimento radicular específico e a relação enxofre-sulfato:enxofre total (S-SO4:St) nas folhas diagnósticas do capim, além de aumentar a atividade da enzima redutase do nitrato e a concentração de amônio nesses tecidos. A dose de enxofre de aproximadamente 1,3 mmol L-1 proporcionou o maior comprimento e superfície radiculares específicos, enquanto a dose mais alta de enxofre (2,5 mmol L-1) maximizou a concentração de enxofre-sulfato e a relação S-SO4:St nas folhas diagnósticas das plantas. Correlações significativas e positivas foram constatadas entre a concentração de nitrogênio total, valor SPAD e a concentração de enxofre total das folhas diagnósticas e a produção de massa seca das plantas, nos dois cortes do capim-piatã. A concentração de nitrogênio nas folhas diagnósticas do capim-piatã e o valor SPAD servem como bons parâmetros para a avaliação do estado nutricional das plantas em relação ao nitrogênio, enquanto para a avaliação do estado nutricional do enxofre nas folhas diagnósticas do capim-piatã, a concentração de enxofre total e a relação Nt:St devem ser tomadas em conjunto.Piatã cultivar of Brachiaria brizantha is a recently released forage grass to be used in brazilian pastures and research on mineral nutrition of this grass is scarce. Nitrogen is the main nutrient to increase forage productivity, but the association with sulphur can influence plant response to fertilization. Through the combination of nitrogen rates with sulphur rates, the objective was to study the morphological, nutritional and productive characteristics of Piatã palissadegrass grown in nutrient solution, by using ground quartz as substrate. The experiment was conducted in greenhouse and five rates of nitrogen (2, 9, 16, 23 and 30 mmol L-1) were combined with five rates of sulphur (0.1, 0.7, 1.3, 1.9 and 2.5 mmol L-1) in a 52 fractionated factorial set in randomized block design, with four replications. Plants were harvested two times, the first harvest was done 44 days after transplanting and the second one was 25 days after the first harvest. The interaction nitrogen rates x sulphur rates was significant for the total number of leaves and tillers, leaf appearance rate, phyllochron, leaf area, dry mass of shoots and roots, SPAD value, root length and root surface, nitrogen and sulphur concentrations in the diagnostic leaves and roots, nitrate concentration and total nitrogen:total sulphur ratio in at least one of the two growth cycles of Piatã palissadegrass. High nitrogen and sulphur rates maximized growth of shoots and roots of the plants. High nitrogen rates resulted in low specific root length and sulfate-sulphur:total sulphur ratio (SSO4: St) in diagnostic leaves, in addition to increasing the activity of the nitrate reductase and ammonium concentration in diagnostic tissue. Sulphur rate about 1.3 mmol L-1 provided the highest specific root length and surface, while the highest sulphur rates (2.5 mmol L-1) maximized sulfate-sulphur concentration and S-SO4:St ratio in diagnostic leaves. There was a significant and positive correlation between the concentration of total nitrogen, SPAD value and total sulphur concentration in diagnostic leaves with plant dry matter production, in both harvests of Piatã palissadegrass. Nitrogen concentration and SPAD value in diagnostic leaves of Piatã palissadegrass can be used as good parameters for assessing the nutritional status of plants in relation to nitrogen, while for the assessment of sulphur nutrition status in diagnostic leaves of Piatã palissadegrass, the concentration of total sulphur and total nitrogen:total sulphur ratio should be taken together

Nitrogen fertilization in sugarcane ratoon: long-term effects of fertilizers and nitrogen rates

O uso de determinadas fontes nitrogenadas, doses e formas de nitrogênio (N) pode aumentar a eficiência de uso de N (EUN) em soqueiras de cana-de-açúcar (Saccharum spp.), mantendo, em longo prazo, elevados índices de produtividade, lucro e proteção ao ambiente. Experimentos de campo e de casa-de-vegetação foram desenvolvidos com os seguintes objetivos: (i) avaliar o efeito do manejo do N-fertilizante e dos ciclos de soqueira da cultura na produtividade, parâmetros tecnológicos, acúmulo de biomassa, acúmulo e balanço de nutrientes e nas alterações dos atributos químicos do solo; (ii) avaliar a produção de biomassa seca, metabolismo e nutrição de plantas de cana-de-açúcar cultivadas em solução nutritiva, com suprimento exclusivo ou misto de nitrato (NO3-) e amônio (NH4+) como fontes de N; (iii) avaliar a EUN do 15N-nitrato (15NH4NO3), 15N-amônio (NH415NO3) e 15N-amida [(15NH2)2CO] aplicados na quarta soqueira de cana-de-açúcar em condições de campo; e avaliar a EUN do 15N-amônio e 15N-nitrato aplicados em mudas de cana-de-açúcar cultivadas em solução nutritiva. No campo, o N-fertilizante foi repetido nas mesmas parcelas experimentais (parcelas estáticas), em anos subsequentes (quatro ou cinco soqueiras) e o manejo de N-fertilizante, que incluiu fontes e doses de N, não influenciou na produtividade de colmos e de açúcar no local 1 (Latossolo Vermelho Amarelo distrófico - LVAd). Entretanto, no local 2 (também LVAd), o NA100 e o NAC100 [nitrato de amônio (NA) e nitrato de amônio e cálcio (NAC), ambos na dose de 100 kg ha-1 de N] foram os manejos mais vantajosos para a obtenção das maiores produtividades de colmo e de açúcar em soqueiras quando comparado aos demais tratamentos. No geral, nos dois locais, o NAC150 (150 kg ha-1 de N) proporcionou os maiores acúmulos de biomassa, N e K nas plantas. Além disso, enquanto o controle (sem adição de N) apresentou as menores produções de biomassa e acúmulos de nutrientes (com exceção ao P), o balanço de nutrientes do solo nesse tratamento foi relativamente neutro após anos de cultivo da cana-de-açúcar. Em condições controladas, plantas de cana-de-açúcar supridas exclusivamente com amônio apresentaram menor produção de biomassa, acúmulo de nutrientes e área foliar do que os outros tratamentos (supridos com combinações de NO3-/NH4+ e somente com nitrato), indicando que o uso exclusivo dessa forma de N não foi eficiente para sustentar o crescimento vegetal. A maior EUN foi obtida com o fornecimento exclusivo de nitrato, que também proporcionou maior produção de biomassa seca, área foliar, acúmulo de macronutrientes, atividade fotossintética e crescimento do sistema radicular. A utilização de 15N indicou que, no campo, não houve diferença na EUN pelas plantas devido à utilização do 15N-nitrato e 15N-amônio. Em contraste, a EUN do 15N-amônio foi maior que a do 15N-nitrato durante o 1º, 4º e 7º dia após a aplicação do fertilizante (DAAF), em condições controladas. Contudo, o uso do 15N-nitrato teve maior EUN nas raízes e planta inteira que o 15N-amônio no 15º DAAF. Isso indica que a cana-de-açúcar pode aproveitar eficientemente as duas formas minerais de N, embora o aproveitamento do amônio seja mais rápido.The use of different fertilizers and rates of nitrogen (N) can increase the N use efficiency (NUE) in sugarcane ratoon (Saccharum spp.), sustaining high yield levels, profitability and environmental protection in long-term. Thus, field and greenhouse studies were performed with the following objectives: (i) evaluate the effect of fertilizer-N management and ratoon crop cycles on sugarcane yield, technological parameters, biomass accumulation, nutrient content, temporal variation in soil chemical properties and soil nutrient balance; (ii) evaluate the biomass production, metabolism and nutrient acquisition of sugarcane plants cropped in nutrient solution, with solely or combined supply of ammonium and nitrate as N sources; (iii) evaluate the NUE of 15N-ammonium (15NH4NO3), 15N-nitrate (NH415NO3), and 15N-amide [(15NH2)2CO] applied to sugarcane under field conditions and the NUE of 15N-ammonium and 15N-nitrate applied to seedlings sugarcane under nutrient solutions. In the field, N fertilizers were replicated in the same experimental plots (static plots) in subsequent years (four or five ratoons) and the management of N-fertilizer, which included fertilizers and N rates, resulted in lack of influence on cane and sucrose yield at Site 1 (Typic Hapludox). However, at Site 2 (also Typic Hapludox), the N treatments AN100 and CAN100 [ammonium nitrate (AN) and calcium ammonium nitrate (CAN), both at a rate of 100 kg N ha-1] provided the highest cane and sugar yield as compared to the remaining treatments. Overall, at both sites, CAN150 (150 kg N ha-1) resulted in the highest biomass accumulation and N and K content by sugarcane. In addition, while the control (no N added) had the lowest biomass accumulation and nutrient content (except for P), the soil nutrient balance in this treatment was relatively neutral, after years of sugarcane cultivation. Under controlled conditions, NH4+-fed plants presented lower biomass accumulation, nutrient content and leaf area than the other treatments (different NO3-/NH4+ ratios and NO3--fed plants), indicating that this N form, when applied solely, was not effective for the proper plant growth. The highest NUE was obtained with NO3--fed plants, which also had the highest production of dry biomass, leaf area, nutrient accumulation, photosynthetic activity, and growth of the root system. The use of 15N-nitrate and 15N-ammonium indicated that there was no difference in NUE by plants in the field. In contrast, the NUE of 15N-ammonium was greater than 15N-nitrate during the 1st, 4th and 7th day after fertilizer application (DAFA), under controlled conditions. However, the use of 15N-nitrate had greater NUE in roots and whole plant than 15N-ammonium in the 15th DAFA. It can be concluded that sugarcane can use both N forms although the recovery of NH4+ was faster than NO3-

Effect of previous soil management on sugarcane response to nitrogen fertilization

N Fertilizer recommendations must be improved to optimize N use efficiency (NUE) for bioenergy crops. A study was conducted to test the hypothesis that sites varying in historical usage of by-product differ in soil N-supplying power and sugarcane (Saccharum spp.) responsiveness to N fertilization. Our aim was to quantify soil N availability and N fertilizer rates, sources, and application timings for their effects on sugarcane yield and NUE. Three N response trials, each involving 0 to 200 kg N ha–1, were conducted in the state of São Paulo, Brazil, at sites varying historically in the usage of vinasse. Before fertilizer application and at harvest, soil inorganic N content was quantified and potential N mineralization estimated by the Illinois Soil Nitrogen Test (ISNT); stalk yield and sugar content were measured at harvest and used to estimate NUE. Sugarcane showed significant response to N fertilization only at the sites with no history of vinasse usage. Reducing the N rate from 120 to 80 kg N ha–1 showed limited potential for lowering yield (~ 1 %), while increasing the NUE by 54 %, which was far better than the 14 % increase achieved by modifying the N source or application timing. Monitoring inorganic N and ISNT levels over time to estimate soil N-supplying power has potential for predicting the responsiveness of sugarcane to N fertilization; however, ISNT interpretations must consider factors that impede mineralization or crop N utilization, such as soil acidity or a limitation on the availability of Ca or P. Soil N testing can help optimize NUE for sustainable bioenergy production

Effect of previous soil management on sugarcane response to nitrogen fertilization

ABSTRACT: N Fertilizer recommendations must be improved to optimize N use efficiency (NUE) for bioenergy crops. A study was conducted to test the hypothesis that sites varying in historical usage of by-product differ in soil N-supplying power and sugarcane (Saccharum spp.) responsiveness to N fertilization. Our aim was to quantify soil N availability and N fertilizer rates, sources, and application timings for their effects on sugarcane yield and NUE. Three N response trials, each involving 0 to 200 kg N ha−1, were conducted in the state of São Paulo, Brazil, at sites varying historically in the usage of vinasse. Before fertilizer application and at harvest, soil inorganic N content was quantified and potential N mineralization estimated by the Illinois Soil Nitrogen Test (ISNT); stalk yield and sugar content were measured at harvest and used to estimate NUE. Sugarcane showed significant response to N fertilization only at the sites with no history of vinasse usage. Reducing the N rate from 120 to 80 kg N ha−1 showed limited potential for lowering yield (~ 1 %), while increasing the NUE by 54 %, which was far better than the 14 % increase achieved by modifying the N source or application timing. Monitoring inorganic N and ISNT levels over time to estimate soil N-supplying power has potential for predicting the responsiveness of sugarcane to N fertilization; however, ISNT interpretations must consider factors that impede mineralization or crop N utilization, such as soil acidity or a limitation on the availability of Ca or P. Soil N testing can help optimize NUE for sustainable bioenergy production